Turbomachinery Mesh Topologies: When to Use H, C, or O-Grids?

The choice of mesh topology directly impacts accuracy, convergence, and computational cost in turbomachinery simulations.

 H-Grid

Structure: Grid lines form an “H” pattern across the domain.

Best Use Cases:

• • Far-field regions where flow is relatively uniform.
  • Simple geometries with minimal curvature.
  • Capturing inlet/outlet boundary conditions in turbomachinery passages.

Advantages:

• • Easy to generate and extend to infinity (good for external flows).
  • Efficient for coarse far-field resolution.

Limitations:

• • Poor resolution near trailing edges and wakes.
  • Not ideal for curved blade surfaces.

C-Grid

Structure: Grid wraps around the trailing edge, forming a “C” shape.

Best Use Cases:

• • Turbomachinery blades with sharp trailing edges.
  • Capturing wake development and downstream flow separation.
  • High-speed flows.

Advantages:

• • Excellent wake resolution behind blades.
  • Smooth clustering near trailing edges.

Limitations:

• • More complex to generate than H-grids.
  • May require hybridization with O-grids near leading edges.

O-Grid

Structure: Grid lines wrap around the blade surface in concentric “O” rings.

Best Use Cases:

• • Resolving boundary layers around curved surfaces (airfoils, turbine blades).
  • Capturing secondary flows in blade passages.
  • Handling strong curvature and tip leakage flows.

Advantages:

• • High-quality boundary layer resolution.
  • Smooth orthogonality near walls → better y+ control.

Limitations:

• • Difficult to extend to far-field without combining with H-grids.
  • More computationally expensive due to clustering near walls.

Key Considerations:

Hybrid Topologies: O-grids near blades, C-grids at trailing edges, and H-grids in the far field are often combined for optimal accuracy and efficiency.

Physics-driven choice: Select topology based on whether the priority is boundary layer resolution (O-grid), wake capture (C-grid), or far-field uniformity (H-grid).

Computational trade-off: O-grids give the best accuracy near walls but increase cell count; H-grids are cheapest but least accurate near complex blade regions.

If anyone would like to share additional information based on their experience, it would benefit CFD users.